1. Field
The embodiments described herein relate generally to radiation-based imaging systems. More particularly, the described embodiments relate to radiation-based imaging systems used in conjunction with radiation therapy.
2. Description
A linear accelerator produces electrons or photons having particular energies. In one common application, a linear accelerator generates a radiation beam and directs the beam toward a target area of a patient. The beam is intended to destroy cells within the target area by causing ionizations within the cells or other radiation-induced cell damage.
Radiation treatment plans are intended to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. To design a radiation treatment plan, a designer must assume that relevant portions of a patient will be in particular positions relative to a linear accelerator during delivery of the treatment radiation. The goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved if the relevant portions are not positioned in accordance with the treatment plan during delivery of the radiation. More specifically, errors in positioning the patient can cause the delivery of low radiation doses to tumors and high radiation doses to sensitive healthy tissue. The potential for misdelivery increases with increased positioning errors.
Conventional imaging systems may be used to verify patient positioning prior to and during the delivery of treatment radiation. Specifically, this verification is intended to confirm that relevant portions of a patient are positioned in accordance with a treatment plan. Some systems may generate, for example, a two-dimensional projection image of a patient portal by passing a radiation beam through the patient and receiving the exiting beam at an imaging system (e.g., a flat panel imager). Other systems produce three-dimensional megavoltage cone beam computed tomography (MV CBCT) images and/or three-dimensional kilovoltage cone beam computed tomography (kV CBCT) images of a patient volume prior to and/or during radiation delivery thereto. Recently-developed systems include linear/arc tomosynthesis and stationary tomosynthesis, which provide three-dimensional images based on fewer projection images than required by CBCT, but usually at poorer resolution.
Online Image-Guided Radiation Therapy (IGRT) refers to techniques in which a patient position is monitored in near real-time during radiation treatment and/or between treatment intervals. These techniques therefore require imaging systems which are capable of generating images quickly. Moreover, the generated images should be suitably detailed to provide accurate evaluation of the patient position. Conventional uses of the above-described techniques fail to satisfy these requirements. In particular, conventional CBCT is too slow and complex, and images generated via tomosynthesis do not exhibit suitable depth resolution.